Vegetable Crop Insect Scouting

David Owens, Extension Entomologist,

Snap Beans and Lima Beans
Scout for potato leafhopper. Sprays are justified if you capture 5 adults or nymphs per sweep. Look very carefully at the bottom of your net, early instar leafhoppers are about the size of a thrips and pale. Good leafhopper materials include Lannate, Dimethoate, pyrethroids, neonics and Sivanto.

Be sure to scout for Colorado potato beetle and spider mites, both of which cause significant injury in a short period of time. Thresholds for a related spider mite species in Southeast Asia are reported as 4-8 per leaf. Should a spray be necessary, we have a bevy of materials for both pest groups. Abamectin will control both, as will premixes containing a diamide like Minecto Pro.

Sweet Corn
We have entered our ‘July lull’ in earworm activity. Counts are lower than they were last week at this time. I expect this period of lower activity to last another 2 weeks. We were not able to run any moths in our vials this week. Thresholds and current trap catch can be found here: Counts from Thursday are as follows:

Trap Location BLT – CEW Pheromone CEW
3 nights total catch
Dover 0 20
Harrington 0 19
Milford 0 2
Rising Sun 0 32
Wyoming 0 6
Bridgeville 0 8
Concord 0 10
Georgetown 0 7
Greenwood 0  
Laurel 1 48
Seaford 0 4
Lewes 0 2
Harbeson   0


Hot dry weather continues favoring mites. Fields that were treated early for mites that came in with transplants seem to have largely controlled those mites, but we are seeing more mites moving in from field margins. If you have powdery mildew, Magister has powdery activity. It is a contact miticide. Be sure to read labels carefully, as many miticides are very limited in terms of number of applications per season.

First generation cucumber beetles are emerging out of the soil quickly. Beetles will often concentrate in flowers and can be easy to spot in them. Unfortunately, there are no established thresholds for beetles once fruit is present. Leps such as cabbage looper and leafroller are beginning to show up in many fields. There are two premixes available for mites and beetles or mites and leps (Gladiator and Minecto Pro), but both contain Abamectin which is very toxic to bees. Read the labels carefully! Assail does a very good job on beetles and has a long residual activity. Diamides do a good job but are primarily worm products, they stop beetles from feeding on treated foliage about week, but once beetles get onto new or fresh foliage or flowers that do not have the material on them, they will resume feeding. Some folks report inconsistent control with pyrethroids, probably due to the relatively long beetle emergence window and the short residual activity of this class.

Scout for squash bug and squash vine borer. You want to wait until squash bug eggs hatch before triggering a spray. They can be controlled with pretty low rates of bifenthrin (per VT testing), and I suspect just about all of the pyrethroids will do a good job. Squash vine borer moths are dayflying moths that lay single eggs on the vine, petioles, and sometimes on the underside of leaves. You may see at the base of leaf petioles a small mound of white frass. This is a sure sign that squash vine borer has already started invading the plant. Small caterpillars can be cut out. Once surgically removed, push some soil over the node and the vine will send out adventitious roots. Some folks have reported some success with injecting Bt into the tunnel site, but I don’t know if anyone has rigorously tested this. If caught early, begin treating vines about once per week with a pyrethroid, preferably in the afternoon after blossoms close for the day to avoid harming bees.

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